A low-altitude flight function, referred to as an LLF function, of the managed type (that is to say, certain data of which are used, such as the path to be followed, are defined by automatic systems and in particular by a flight management system (FMS)) is also known. This function, which is on board an aircraft, allows the crew to fly the aircraft under automatic guidance control at a low level of as little as 500 feet above the ground in instrument flight conditions. The automated flight device guides the aircraft along a three-dimensional path established by the flight management system (FMS), taking into account the lateral flight plan, the terrain over which said aircraft is flying, performance of the aircraft and parameters input into the FMS system by the crew.
An LLF phase (or LLF operation) corresponds to a continuous portion of the flight plan along which the crew would like to fly according to an LLF function. In order to produce an LLF phase, the pilot therefore has to input a plurality of parameters that are specified below, referred to as phase parameters.
The pilot also has the option of defining successive sections within the LLF phase using parameters that are also specified below, referred to as section parameters. Once the set of parameters is set and the structure of the LLF sections is defined, the FMS system can calculate the three-dimensional path that the aircraft will follow.
Once the LLF phase has been defined by the crew and established by the FMS system, the pilots have the option of applying the following modifications to the path, before or during the flight:                a lateral modification to the path (by requiring the aircraft to fly directly towards a waypoint by inserting a new waypoint or deleting a waypoint);        a modification to the parameters set during the process of defining the LLF phase (with the exception of certain phase parameters when the corresponding phase is followed).        
However, the LLF function does not allow the crew to separate an existing LLF phase into two in order to obtain two separate phases while maintaining their structure, in particular for inserting an intermediate section between these two parts.
The above-mentioned modifications allow an LLF phase to be shortened by selecting a new phase entry or exit waypoint. However, the second part of the LLF path is then lost, as well as its structure. In order to retrieve this second part, it is necessary to integrally reconstruct a new LLF phase by re-inserting the same parameters after the intermediate section.